1. Field of the Invention
The present invention relates to a phosphor which emits light by electron beam excitation, and particularly to a phosphor which can be favorably used for a color display device using an electron beam, such as a color cathode-ray tube and a field emission display (hereinafter, described as “FED”).
2. Description of the Related Art
A phosphor for electron beam excitation, which emits light by being excited by the electron beam, is conventionally used for a color cathode-ray tube, and is further used for an FED which is a thin planar display which has been developed in recent years. As phosphors for electron beam excitation used for a color display device such as a color cathode-ray tube and an FED, ZnS:Ag,Cl is known as a blue phosphor, and ZnS:Cu,Al is known as a green phosphor. Y2O2S:Eu3+, Y2O3:Eu3+, YVO4:Eu3+ and the like are known as red phosphors, and among them, Y2O2S:Eu3+ is widely used in the existing color cathode-ray tubes for the reason of excellent light emission color and high brightness.
Corresponding to the demand for enhancement in definition and contrast of a display image for the recent color cathode-ray tubes, the measures for increasing the density of the electron beam which is irradiated to the phosphors is taken, but in the case of using Y2O2S:Eu3+ as a red phosphor, the phenomenon, which is called brightness saturation, in which brightness is saturated when the rise in the brightness reaches a fixed degree or higher, occurs, even if the density of the electron beam is increased. This is considered to be because a temperature quenching phenomenon occurs in the red phosphor due to a rise in temperature of the phosphor film. The brightness saturation phenomenon causes that problems that the emission efficiency of the red phosphor in the color cathode-ray tube is reduced, image degradation of the display screen occurs during operation of the color cathode ray, and chromaticness of white color displayed in mixed color of RGB is changed significantly due to reduction in brightness in red light.
Several proposals are made to prevent the saturation phenomenon of the brightness, and there is the description that the occurrence of the brightness saturation is decreased by doping a very small amount of Tb3+ or Pr3+ to Y2O2S:Eu3+, for example, in Non-patent Document 1. Patent Document 1 makes proposal to enhance brightness by doping a very small amount of one or both of Tb3+ and Pr3+, and Ca to Y2O2S:Eu3+, and Patent Document 2 makes a proposal to enhance brightness by doping a very small amount of one or both of Tb3+ and Pr3+, and one or both of Sm and Nd to Y2O2S:Eu3+.
[Non-patent Document 1] page 172 to page 176 of “Phosphor Handbook” (compiled by Phosphor Research Society, published by Ohmusha, Ltd., 1987)
[Patent Document 1] Japanese Patent Application Laid-open No. 2003-13059
[Patent Document 2] Japanese Patent Application Laid-open No. 2000-73053
However, in the cathode-ray tubes which are used in a high-definition television, a high definition computer display and the like which are the color display devices of recent years, making the phosphors finer particles is demanded to achieve enhancement in definition and contrast of the displays. With this, density of the electron beam irradiated to the phosphors tends to increase, and therefore the brightness saturation occurs even in the case of using the aforementioned improved Y2O2S:Eu3+ phosphor to make it difficult to obtain sufficient brightness, thus causing the problem of reducing brightness and color balance of the screen due to insufficient brightness in red light to make it difficult to obtain high-definition screen.